Hadronic Physics III
Geant4 Tutorial at
Marshall Space Flight Center
19 April 2012
Dennis Wright (SLAC)
Geant4 9.5
Outline
• Gamma- and lepto-nuclear models
• based on CHIPS model
• based on Bertini
• QCD string models
• Quark-gluon string (QGS) model
• Fritiof (FTF) model
• Other models
• CHIPS
• capture
• fission
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Gamma- and Lepto-nuclear Processes
• Geant4 models which are neither exclusively electromagnetic
nor hadronic
• gamma-nuclear
• electro-nuclear
• muon-nuclear
• Geant4 processes available:
•
•
•
•
G4PhotoNuclearProcess (implemented by two models)
G4ElectronNuclearProcess (implemented by one model)
G4PositronNuclearProcess (implemented by one model)
G4MuonNuclearProcess (implemented by two models)
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Gamma- and Lepto-nuclear Processes
• Gammas interact directly with the nucleus
• at low energies they are absorbed and excite the nucleus as a
whole
• at high energies they act like hadrons (pion, rho, etc.) and form
resonances with protons and neutrons
• Electrons and muons cannot interact hadronically, except
through virtual photons
• electron or muon passes by a nucleus and exchanges virtual
photon
• virtual photon then interacts directly with nucleus (or nucleons
within nucleus)
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Gamma- and Lepto-nuclear Models
Gamma-nuclear
Lepto-nuclear
e-
virtual 

 s and nucleons
s and nucleons
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Gamma- and Lepto-nuclear Models
• G4VDMuonNuclear
•
•
•
•
Bertini cascade at low and medium energies (E < 10 GeV)
FTFP at high energies (E > 10 GeV)
for both constituent models gamma is treated as a pion
will soon have direct gamma interaction
• G4GammaNuclearReaction
• alternate to G4VDMuonNuclear
• based on CHIPS (chiral invariant phase space) model
• direct gamma interaction
• G4ElectroNuclearReaction
• CHIPS-based model for electrons, positrons
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QCD String Models
• Fritiof (FTF) valid for
• p, n, , K, , from 3 GeV to ~TeV
• anti-proton, anti-neutron, anti-hyperons at all energies
• anti-d, anti-t, anti-3He, anti- with momenta between 150
MeV/nucleon and 2 GeV/nucleon
• Quark-Gluon String (QGS) valid for
• p, n, , K from 15 GeV to ~TeV
• Both models handle:
•
•
•
•
building 3-D model of nucleus from individual nucleons
splitting nucleons into quarks and di-quarks
formation and excitation of QCD strings
string fragmentation and hadronization
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How the QCD String Model Works (FTF Case)
• Lorentz contraction turns nucleus into pancake
• All nucleons within 1 fm of path of incident hadron are
possible targets
• Excited nucleons along path collide with neighbors
•n + n  n, NN, 
•essentially a quark-level cascade in vicinity of path  Reggeon
cascade
• All hadrons treated as QCD strings
•projectile is quark-antiquark pair or quark-diquark pair
•target nucleons are quark-diquark pairs
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How the QCD String Model Works (FTF Case)
• Hadron excitation is represented by stretched string
• string is set of QCD color lines connecting the quarks
• When string is stretched beyond a certain point it breaks
• replaced by two shorter strings with newly created quarks, antiquarks on each side of the break
• High energy strings then decay into hadrons according to
fragmentation functions
• fragmentation functions are theoretical distributions fitted to
experiment
• Resulting hadrons can then interact with nucleus in a
traditional cascade
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High Energy Nuclear Interaction
nucleon
projectile
excited string
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QGS Validation
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FTF Validation
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FTF Anti-deuteron Scattering
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CHIPS (Chiral Invariant Phase Space) Model
• Model originally used to de-excite nuclei after high energy
interaction
• has since been extended for use in stopping processes and
gamma- and electro-nuclear models
• experimental versions apply to high energy and ion-ion
• Basic model principles:
• u, d, s quarks all treated as massless (hence chiral invariant)
• when two hadrons interact, a bag of partons is formed, all of
which are distributed uniformly in phase space
• this bag is called a “quasmon” and decays somewhat
thermodynamically as partons fuse to form hadrons
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- Stopping in Nucleus (CHIPS)
quasmon
clusters of
nucleons

hadron
escapes
nucleus
nuclear
evaporation
begins
quasmon
disappears
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Capture Processes and Models
• G4PionMinusAbsorptionAtRest
• process with direct implementation (no model class)
• G4PionMinusAbsorptionBertini **
• at rest process implemented with Bertini cascade model
• G4KaonMinusAbsorption
• at rest process with direct implementation
• G4AntiProtonAnnihilationAtRest
• process with direct implementation
• G4FTFCaptureAtRest **
• process implemented for anti-protons by FTF model
** recommended
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Capture Processes and Models
• G4MuonMinusCaptureAtRest
• process with direct implementation (no model class)
• G4QCaptureAtRest
• alternative to above, using CHIPS model
• G4AntiNeutronAnnihilationAtRest
• process with direct implementation
• G4HadronCaptureProcess
• in-flight capture for neutrons
• model implementations:
• G4LCapture : all incident energies
• G4NeutronHPCapture (below 20 MeV)
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Fission Processes and Models
• G4HadronFissionProcess can use two models
• G4LFission (mostly for neutrons)
• G4NeutronHPFission (specifically for neutrons below 20 MeV)
• A third model handles spontaneous fission as an inelastic
process (rather than fission)
• G4FissLib: Livermore Spontaneous Fission
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Isotope Production
• Special process originally designed to register recoil nuclei
after any interaction
• Now mostly outdated except if you use the LEP models
• those models don’t produce recoil nuclei
• Now implemented as a model running specifically with LEP
code
• To use:
G4LENeutronInelastic* nmodel = new G4LENeutronInelastic;
G4NeutronIsotopeProduction* prodModel =
new G4NeutronIsotopeProduction;
nmodel->RegisterIsotopeProductionModel(prodModel);
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Summary
• Gamma-nuclear and lepto-nuclear processes are available for
nuclear reactions initiated by non-hadrons
• Two QCD string models are available for implementing high
energy interactions
• Fritiof (FTF) : the more versatile, covers many particle types,
larger energy range
• Quark-Gluon String (QGS)
• Several stopping processes and models available
• for , , K, anti-p, anti-n
• CHIPS for stopping and nuclear de-excitation
• Capture and fission (mostly for neutrons)
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